In controlling the activation of a machine it is common to employ a digital computer, special purpose computational circuits, or microprocessor. The digital computer is typically a microprocessor which is dedicated by firmware to cause the activation of a variety of functions. Such components, microprocessors, and special purpose computational circuits will be referred to herein generally as “controllers”.
One form of programmable control activation includes a centralized control unit that monitors environmental sensors and inputs from user controls to maintain a schedule of pre-programmed time-of-day and day-of-the week events. Inputs to the central control are provided by dedicated low-voltage wiring, signals carried on power lines, RF signals, signals on existing telephone wiring and, occasionally, optical signals. The central control unit is controlled by a program that is either specifically built for the particular installation or a general-purpose program with a user interface that allows operator to make certain types of modifications.
Where the controller contains a first processor for controlling a machine or device and a second processor controls the first processor, the first processor will be referred to as a “slave” processor and the second processor will be referred to as a “master” processor. In a master-slave system, there is ordinarily a random access memory (“RAM”) associated with each processor and at least one mass storage device, such as a magnetic disk, associated with the system. The system also typically includes an input device, such as a keyboard associated with the master processor, and a visual output device such as a cathode ray tube (“CRT”) display or a printer. In programmable controlled activation it is often desirable to change the programmed controller software in order to perform different functions, such as data evaluation or output functions. The software typically comprises several functionally distinct parts, such as parts for performing human interface, circuit control, file storage, and computational functions. Sometimes these parts are divided between different programs or distributed between the controllers. In particular, in a master-slave system, the computational function is ordinarily performed by a program in the slave processor, while a program in the master processor ordinarily performs the human interface function.
In one example of a computational function, controllers have been employed in heating, ventilating and air conditioning systems to monitor and regulate the positions of damper and valve actuators for controlling airflow and fluid flow in air handling units and to monitor the signal values of temperature and humidity sensors and regulate their related set points. Generally, such systems employ a centralized processing unit acting as a master having operator display and manual control functions as well as computational and command-generating capabilities. Additionally, the centralized processing unit embodies a library of computer software programs arranged in a relatively complex programmer language for providing energy management functions like temperature set back in office buildings during non-peaked hours and for limiting total load demand during peaked hours. These centralized processing units are commonly termed head end units and are operably coupled at the first or highest hierarchical level in a building environment system. The farther down you move in this hierarchical structure the less flexible the units are to program because of their limited capabilities. The head end units often control and monitor hundreds of individual datum points within an environmental system. For example, the position of actuators used for damper and valve positioning and the output signals of temperature and humidity sensors used for providing feedback data relating to those parameters are examples of such datum points.
In addition to the central processing unit automated networks are often employed with a plurality of second level data processing units operably coupled to the head end unit for performing certain tasks which would otherwise be required to be performed by the latter. As an example, a data processing unit may perform information-checking functions with respect to signals passing between data points and the head end unit. Such data checking may include, for example, the detection of alarm signals or the detection of temperature changes that exceed predetermined values. Each data processing unit may, in turn, have a plurality of third level field processing units operatively coupled to it for performing analog to digital conversion and limited processing functions. This pushing down of functions to downstream data processing units, however, increases the likelihood of errors and makes recovery dependent upon the functionality of other data processing units.
The above system customarily employ actuators for the manipulation of valves used to control the flow of fluid and heater coils. Because digital signals from a field processing unit are often incapable of directly powering these actuators, it may be necessary to provide a separate, power amplifying and signal transducer equipment interface panel immediately adjacent each of the units. These interface panels receive digital signals from the associated field processing unit and responsively provide pneumatic or electrical power at levels sufficiently high to position the actuators mechanically coupled to the dampers or valves.
While the aforementioned arrangements for controlling a device or unit are in wide use, they tend to be characterized by certain disadvantages. In particular, the head end central processing unit may be subject to periodic failures. In the event of a failure of the centralized processing unit, the entire system or major portions thereof may be disabled. The field processing units are frequently incapable of algorithmically processing received information and generating commands or other signals based thereon. Field processing units have limited utility in that they contain no computer programs, either in single or selectable library configuration, for continuously performing optimized control functions in a stand alone mode or for permitting a local operator to select and modify an aspect of a program routine to meet the requirements of locally-changed environmental conditions or for that matter conditions that require close monitoring and a real time response. Another disadvantage of field processing units of the known type is that their control capability is frequently degraded when functioning in a standalone mode by reason of the failure of equipment related to the head end unit. In particular, they are configured to retain actuator positions at settings that existed immediately preceding a fault rather than to continue to monitor and control positions for optimized energy management and occupant comfort. An additional limitation of the prior art systems is that there are often an equal number of power sources for each of the power signal conditioners, controllers, analog to digital converters, and the controlled unit. A failure in one power source can lead to a breakdown of the overall system.
For the reasons set forth above there is a need for a self-contained controller that can monitor environmental parameters, generate electrical power upon the occurrence of a triggering event, and operates on a single power source.